1. Field of the Invention
The present invention generally relates to a solid state image pickup element, and particularly relates to a solid state image pickup element for a color picture.
2. Background of the Invention
A solid state image pickup for a color picture typically comprises, as shown in FIG. 1, an MOS image sensor 10 constituted by photoelectric conversion elements 12 arranged in a matrix, vertical switches 14 associated with the respective photoelectric conversion elements 12, horizontal switches 16 associated with each column of the vertical switches 14, a vertical shift register 18 for controlling the vertical switches 14, and a horizontal shift register 20 for controlling the horizontal switches 16. Color filters having colors respectively corresponding to picture elements are provided over the photosensitive conversion elements 12 (and possibly covering other elements) constituting the image sensor 10.
The terms of "an image sensor" and "a solid state image pickup element" are originally used to indicate one and the same device. In this specification, however, a semiconductor element for monochromatic light is specifically referred to as "an image sensor" and an image sensor which is provided with color filters so as to be used for a color picture is referred to as "a solid state image pickup element."
In a photometric sensor for three primary colors such as red (R), green (G), and blue (B), a light reception portion is constituted by M.times.N multi-element units. In this case, the signals from each of those units are subject to signal processing as if each unit is located at a single respective point for the photometering although each unit is composed of an assembly of photoelectric conversion elements 12 slightly displaced from each other. Each of the units is constituted by a plurality of picture elements, each of the picture elements being provided with color filters for R, G, and B. Therefore, in each unit, a plurality of photoelectric conversion elements 12 provided for each color may collectively generate a single output. In the case where a plurality of photoelectric conversion elements 12 are provided for each color in each unit, a sum of outputs of those photoelectric conversion elements for each color is produced as a single output.
In the conventional MOS-type solid state image pickup element, as shown in FIG. 1, respective outputs of photoelectric conversion elements 12 are successively sent out and temporarily stored in a memory in an external circuit, so that a sum of the output signals for each color in each unit is formed in the external circuit.
The external circuit including the memory means is complicated in structure, requires a large number of parts, and is therefore expensive.
If the photoelectric conversion elements 12 in each of units are suitably adjusted in shape and size thereof so as to put weights on signals of the respective colors, on the other hand, it becomes unnecessary to provide a plurality of photoelectric conversion elements for each of the colors. This arrangement, however, has difficulties in manufacturing, resulting in increase in cost similarly to the foregoing cases.